Polymers are transformed into fibers through a process called spinning, which involves melting or dissolving the polymer into a solution. The most common methods are wet spinning, dry spinning, and melt spinning. In wet spinning, the polymer is dissolved in a solvent and extruded through a spinneret into a coagulation bath, where the solvent is removed, leaving behind the solid fiber. Dry spinning also involves dissolving the polymer but the solution is extruded into warm air, allowing the solvent to evaporate and the fibers to solidify. Melt spinning is used for polymers that can be melted and involves extruding the melted polymer through a spinneret and cooling it down to form solid fibers. These fibers can then be drawn or stretched to align the polymer molecules, enhancing strength and flexibility. The process chosen depends on the polymer's properties and the desired characteristics of the final fiber.

In protein structure, glycine and proline are the amino acids most favored in turns. Glycine is highly flexible due to its small size, lacking a side chain beyond a hydrogen atom, which allows it to fit into the tight angles of turns without steric hindrance. Proline, on the other hand, has a unique cyclic structure that restricts its backbone rotation, making it act as a structural pivot, facilitating the sharp turns found in protein structures. These turns are crucial for the overall folding and stability of proteins, allowing them to adopt their functional three-dimensional shapes. While other amino acids can be found in turns, glycine and proline are particularly well-suited for these positions due to their structural characteristics.

Low-density polyethylene (LDPE), widely used in plastic bags, containers, and packaging films, generally does not contain Bisphenol A (BPA). BPA is more commonly associated with polycarbonate plastics and epoxy resins, used in the manufacturing of hard, clear plastic products and the lining of metal cans, respectively. LDPE is favored for its flexibility, chemical resistance, and safety in food contact applications. Regulatory agencies, like the FDA, monitor and regulate BPA use in products that come in contact with food, but given LDPE's typical BPA-free status, it's considered a safer choice for consumers concerned about BPA exposure. Nevertheless, consumers seeking to minimize plastics use in food storage and packaging often explore alternative materials such as glass or stainless steel to eliminate potential chemical exposure risks entirely.